When control signal reaches threshold the compressor C1-Sigma starts gain reduction very slowly thus most attack of the signal passes through (effect transient shaping). The curve of signal level change in this mode is similar to σ-function and due to that this attack mode is also called «sigmoid».

C1-Sigma compressor is not an emulation of any hardware or software compressor. But due to the sigmoid attack mode of audible results, it can be compared with the compressor Neve 33609 (on «drum buss»).